What Can We Learn from Cases of Internal Mammary Artery Damage in Coronary Artery Bypass Graft?
Coronary artery bypass graft (CABG) surgery is a widely performed procedure to restore blood flow to the heart in patients with coronary artery disease. The internal mammary artery (IMA) is the preferred conduit for CABG due to its superior long-term patency rates compared to other grafts. However, IMA damage during harvesting remains a significant concern, as it can compromise the success of the surgery and lead to adverse outcomes. This article explores the lessons learned from 286 cases of IMA damage recorded over a 20-year period in 10,360 CABG operations, providing valuable insights and recommendations for surgeons.
Incidence and Causes of IMA Damage
Between July 1997 and April 2017, 286 cases of IMA damage were documented, representing an incidence rate of 2.7%. This relatively high incidence is attributed to the surgeons’ experience and the learning curve associated with IMA harvesting. Although all operations were performed by a single experienced surgeon, the procedures were conducted in various hospitals with the assistance of over 200 young and inexperienced surgical assistants. This highlights the importance of proper training and experience in minimizing IMA damage during CABG.
Key Recommendations for Preventing IMA Damage
Based on the analysis of these cases, several practical recommendations have been formulated to help young surgeons avoid IMA damage:
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Understanding LIMA Anatomy: The left internal mammary artery (LIMA) is the most commonly used IMA in CABG. Surgeons must be aware of its anatomical variations, particularly when the LIMA is tightly adhered to the sternum or significantly kinks. These characteristics increase the risk of damage during harvesting.
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Optimal Coagulation Power: It is recommended to use a coagulation output power of 20 W during IMA harvest. This setting balances effective hemostasis with minimizing thermal injury to the artery.
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Electrocautery Precautions: Electrocautery should be kept at least 0.5 cm away from the IMA, and its use should be as brief as possible. Radiosurgery is preferred over electrosurgery for IMA harvesting, as it is less traumatic and reduces the risk of thermal damage.
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Avoiding Thermal Damage from Clips: If a clip has been placed on a branch of the IMA, using electrocautery nearby can cause thermal damage conducted by the clip. Surgeons are advised to use scissors instead or avoid touching the clip with the electrocautery.
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Intraluminal Operation Caution: Procedures such as using metal probes or injecting papaverine to dilate a spastic IMA can lead to IMA dissection. These techniques should be avoided or used with extreme caution.
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Heparinization Before Clamping: The Bulldog clamp should not be used to clamp the IMA before full heparinization, as this can lead to thrombosis.
Management Strategies for IMA Damage
The study outlines a protocol for managing IMA damage based on the pathological cause and injury location. The following strategies were employed:
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Proximal Damage: For damage caused by endothelial disruption or stenosis, free IMA grafts were used to repair the proximal injury.
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Distal Damage: Skeletonized IMA or a combination of the IMA and the great saphenous vein (GSV) was used to address distal damage.
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Middle Damage or Dissection: In patients older than 60 years, the GSV was used instead of the IMA for middle damage or dissection. For younger patients, the radial artery (RA) or right IMA (RIMA) was used, depending on the narrow position of the left anterior descending artery (LAD).
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Bleeding IMA: Direct suturing or a GSV patch was applied to control bleeding. Free IMA grafts were also used when the IMA length was insufficient.
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Potential Damage Assessment: If the LIMA-LAD pulsatility index (PI) exceeded 5 and the flow was less than 15 mL/min (measured using transit-time flow measurement), an additional GSV graft from the aorta to the LAD was applied.
Postoperative Outcomes and Adverse Events
The study reported several postoperative complications, including one death due to extensive thrombosis in the LIMA and GSV grafts, two cases of cerebral infarction, and one acute cardiac infarction occurring four hours postoperatively. An intra-aortic balloon pump was used in two cases, and one minimally invasive incision was converted to a normal sternum incision. Additionally, one off-pump CABG (OPCAB) procedure was converted to on-pump CABG due to ventricular fibrillation during anastomosis of the GSV to the posterior descending artery (PDA). Overall, adverse events occurred in eight cases (2.8%), with seven being major adverse cardiovascular and cerebrovascular events (MACCEs).
Minimally Invasive Techniques and Conversion to Sternotomy
The rise of minimally invasive direct CABG (MIDCAB) and robotic endoscopic CABG (RobECAB) techniques has introduced new challenges in managing IMA damage. When LIMA damage occurs during minimally invasive procedures, conversion to a normal sternum incision is often necessary, reducing the benefits of minimally invasive techniques. To avoid this, a management protocol was proposed based on the location of LIMA injury: axillary bypass for proximal LIMA, a shunt for mid-LIMA repair, and extension for distal LIMA.
Long-Term Follow-Up and Patency Rates
Although long-term follow-up data is limited, one case demonstrated excellent flow in the LIMA and GSV conduit eight years postoperatively, suggesting that this method may be effective in preserving the LIMA when its length is insufficient. Another case revealed stenosis at the injured site six months postoperatively, leading to the adoption of free IMA grafts for injuries exceeding half the IMA’s diameter rather than direct suturing.
Conclusion
The study provides a comprehensive protocol for preventing and managing IMA damage during CABG, emphasizing the importance of surgical experience, anatomical understanding, and careful technique. By following these recommendations, surgeons can reduce the incidence of IMA damage and improve patient outcomes. The findings also highlight the need for further research into long-term patency rates and the effectiveness of alternative grafting strategies in cases of IMA damage.
doi.org/10.1097/CM9.0000000000000023
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